Mihai Mocanu was born on 24 February 1942 in Constanța, Romania, starting to play football in 1952 at local club, Locomotiva, afterwards going to play for Rafinăria Câmpina, returning to his hometown at Electrica where he finished his junior career, starting his senior career in Divizia B, playing for two seasons at SNM Constanța, afterwards going for one season at fellow Divizia B club, Chimia Făgăraș.

[3][4][5][6] He went to play for Petrolul Ploiești, making his Divizia A debut on 25 August 1963 in a 2–1 away loss in front of UTA Arad, making a total of 201 appearances with six goals scored in the competition over the course of nine seasons in which he also helped the Yellow Wolves win the 1965–66 Divizia A, being used by coach Constantin Cernăianu in 26 matches.

[3][4][5][7][9][10][11] After he made his last Divizia A appearance for Petrolul on 12 December 1971 in a 1–0 home loss against Jiul Petroșani, Mocanu went to play in Cyprus at Omonia Nicosia for two seasons with fellow Romanian, Constantin Frățilă, winning the title and the cup in 1974.

[3][4][5][6][7][9] Mihai Mocanu played 31 games at international level of Romania, making his debut on 1 June 1966 under coach Ilie Oană in a friendly which ended with a 1–0 loss against West Germany.

[1][13] He went on to play four games at the Euro 1968 qualifiers and two at the successful 1970 World Cup qualifiers, being used at the final tournament by coach Angelo Niculescu in all the minutes of the three group matches as Romania did not advance to the next stage and had a appreciated performance in the 3–2 loss against Brazil in the duel with his direct opponent, Jairzinho.